ABSTRACT
Accepted practice for the computation of steady water surface profiles is that it is necessary to alter the direction of the calculation when the flow becomes super-critical. The origin of this limitation appears to be in the common practice of writing the flow equations as an explicit ordinary differential equation. This paper demonstrates by some test cases, however, that retaining the flow equations in their implicit form allows trans-critical flows to be computed by a backwater method. Finally the implications of these results for practical river modelling are discussed.
